1. Technical Field
The present invention relates to a contents alteration detection apparatus and a method thereof for embedding authentication data including copyright information imperceptibly in contents data such as image data and detecting which part of the contents alteration was added to by using the embedded authentication data.
2. Prior Art
For instance, International Publication No. WO97/49235 discloses a method for embedding copyright information and so on (hereafter, also generally referred to as authentication information) in contents data such as image data by pixel block coding (PBC) in a visually imperceptible manner (hereafter, the manner of imperceptibly embedding an authentication method in contents data is also referred to as the “electronic watermarking method”).
In addition, International Publication No. WO98/116928 discloses a method for prohibiting alteration of image data to effectively protect publications by applying the electronic watermarking method disclosed in WO97/49235 and so on.
Furthermore, Japanese Unexamined Patent Publication No. Hei10-164549 discloses a method for detecting alteration of image data by improving the electronic watermarking method disclosed in WO97/49235 and so on so as to embed authentication information in image data in an integral and inseparable manner.
Moreover, in addition to these documents, Japanese Unexamined Patent Publications No. Hei09-151747, Hei10-83310, Hei10-106149, Hei10-161933, Hei10-164349, Hei10-285562, Hei10-334272, Hei-240626, Hei10-240129 and so on also disclose inventions related to the electronic watermarking method.
By the methods disclosed in these documents, authentication information is embedded using a hash function and so on to detect whether or not alteration being added to image data. If alteration is performed by using a hash function to a part of image data in which authentication information is embedded, this alteration influences the entire image data. Thus, while this method can detect alteration being added to some part of image data, it cannot concretely detect and indicate which part of the image data the alteration is added to.